Entries have closed for the November Slot 6 "Checked versus Unchecked" and the Slot 7 "Unchecked versus Checked".
Submitted comments make it clear that quite a few members are unaware of this specific terminology with regards to crossword puzzles.

The Chambers dictionary actually defines:

checked square n a square in a crossword that belongs to the solution of two clues.

unchecked adj (of a square in a crossword puzzle) holding a letter that forms part of one word-solution only

In other words, checked letters are where Across and Down answers intersect. Unchecked letters belong to an Across or a Down answer, but not both.

In the Slot 6 puzzle, every checked letter is a consonant whereas every unchecked letter is a vowel. Then, as expected, the Slot 7 puzzle has the opposite pattern.

As an example, the Slot 7 puzzle has as its core the answer ALUMINO-SILICATE which I believe is the only possible 15-letter option in existence with the required alternating vowel/consonant structure. Thankfully, it could be clued conveniently.